Method and means fob inductively



. I I Jan. 16, 1940.

RAVA 4 METHOD AND MEANS FOR INDUCTIVELY HEATING THE METALLIC PARTS- OF ENCLOSED ELECTRICAL DEVICES Original Filed May 29, 1924 fl/exmmer Emm- 1 INVENTOR.

Realms Jan. 16,1940

UNITED STATES PATENT-Q OFFICE.

LIETHOD AND MEANS FOR INDUCT'IVELY HEATING THE METALLIC PARTS OF EN- CLOSED ELECTRICAL DEVICES Alexander Rava, Chicago, 'Ill.

Original No. 1,676,049, dated July 3, 1928 Serial- No. 716,632, May'29, 1924.

Application for reissue February 2, 1934, Serial No. 709,517

metallic and other getters for the purpose of cleaning up the residual gases within the bulb where, as, for example, in a radio vacuum tube,

1 a high vacuum is desirable and it is immaterial whether or not the glass walls remain transparent. This indeed is the common practice at the present day in the manufacture of high vacuum devices that depend on electronic discharge.

15 It has also been proposed to introduce a gas filling within the bulbs of rectiflers, detectors of certain types and other devices ofv like nature. Again gases that react with oxygen have been introduced into devices that are provided with electrodes or other metal parts within the 'bulb either in a vacuum or in an atmosphere of gas, for the purpose of preventing the oxidization of the metallic parts. It has also been suggested that a nitrogen atmosphere may be created within the envelope or bulb. as in a gas filled incandescent lamp, by vaporizing nitrogen bearing compounds, as, for example, phosphorous nitride, after sealing of the bulb. It is also a .frequent practice in the radio vacuum tube art to heat the electrodes to drive out the occluded gzlsss from the metal during exhaustion of the There has never been suggested, however, any entirely satisfactory method of vaporizing these substances or heating the electrodes at a desired time. In the case of radio vacuum tubes ma nesium for example is commonhr vaporized within the envelope by bombardment while the tube is being exhausted or, by inductive heating while the tube is still on the pumps. The heating of the metal parts, either inductively or by bombardment is primarily for the purpose of driving out the occluded gases. In neither instance is a it possible to control the time at which the vaporization shall take place as it occurs whenever the temperature of the metal parts has been raised to the vaporization point of the material that is desired to be volatilized. This val0 porization point is generally a low temperature yet the gettershould not be vaporized until the occluded gases have been driven out of the metal parts, an operation that requires a very much a higher temperature.

Itistheobieotoftbepreaentinventionto provide a method and means for inductive heating of the metalparts of electrical devices inclosed in an envelope, whereby the occluded gases are driven off from the metal parts by .one heating, and vap orizable material, such as I metallic getters for example, or other gas producing materials, will be volatilized by another. In accordance with my invention, I make use of the principleembodied in Faradays law. The

high frequency magnetic flux employed in in 10 ductive heating is produced generally by a cylindrical coil, through which a strong current of several hundred kilocycles is passed. The direction of the main flux-in the spacesurrounded by the coil and in the immediate external proxll imity thereto is parallel to the geometrical axis of the coil. If, now, a closed flat conducting contour or loop is placed in the path of the flux so that the plane of the contour or loop is perpendicular to the direction of the flux, a poweran ful electromotive force is induced in the loop. This electromotive force is directly proportionate to the size of the suriace inclosed by the contour of the loop. If, however, the contour is parallel to'the flux the induced electromotive force will 35 be negligible.

In accordance with my invention, 1 weld upon the metal part which is to be heated, a loop of conductive material in such position as may be desired to carry out the objects of this'invention. so

This loop may present a completely inclosed contour in itself, or it may be so attached to a metal part, as, for example, the grid of a radio vacuum tube, that the inclosed contour will be formed partly by the loop and partly by the coil 35 of the grid to which it is attached.

The, accompanying drawing shows the use of my invention to one particular form of apparatus to which it is'applicable, namely, a radio vacuum tube. Figure 1 shows the method of using it go for the purpose of driving out the occluded gases from the grid of the tube. Figure 2 shows the the same letters indicate similaf parts 0! the 59 device it will be observed that I have shown a well known type of radio vacuum tube in which the grid, A, is of elliptical coil construction. The plate electrode, 18, is also of the equally familiar box construction. I have found by actual exll periment that such'a structure presents considerable obstacles to the degasification of the electrodes by inductive heating. found in fact that when vacuum tubes having a grid and filament electrodes enclosed within a plate electrode have, been inductively heated to remove the gases therefrom, they differ widely in their behavior, showing in general a low electronic emission and poor amplifying properties.

This is particularly so when they are used as high frequency amplifiers. I have discovered that these defects are due to an insuflicient degasification of the grid electrode, the bars and supports of which, being shielded bythe surrounding plate, cannot be degasified properly by the present method of inductive heating. It is also particularly the case that in the present methods of inductive heating, the getter is volatilized too soon and if the heating is continued after such volatilizationmore gases are driven out of the metal parts which can no longer be counteracted by the getter and such gases therefore remain free within the bulb unless the exhaust pumps succeed in removing them.

-By Faradays law, the loop formed as above described when its plane is perpendicular to the direction of the magnetic flux from the high frequency coil, will cause a thorough heating of the part to which it is attached. In Figure 1 it will be observed that the loop, 0, is mounted on the supports D and D" which may be extensions of the grid supports. The shape of the loop, however, is such that it extends outward from these supports over the plate the contour of which it in part follows but from which it is insulated.

The plane of this loop is parallel to the plane of the lateral section of the plate. The loop so mounted does not present in itself a closed contour since it is open at one side. The half of the coils of the grid at the open side of the loop, however, complete the contour so that the same is eflectively closed. When the high frequency coil is brought down over the bulb of such a tube' the magnetic flux induces a current in the plate which will bring it to a high heat in the same manner as is usual in the processes of such heating as well known at the present time. But it will also induce a current in the grid which will produce a similar heating of that electrode. If the loop were absent, this result would be prevented by the shielding effect of the plate. The loop, however, overcomes this shielding eifect by reason of the fact that the high frequency coil in duces a current in the grid by reason ofthe fact that the grid itself forms part of the closed contour of the loop. The current is, therefore, set up with equal effect in the grid and the plate simultaneously, and the result is an equal heating and degasification of both.

In Figure 2 it will be observed that the loop, instead of being mounted in a plane parallel to the plane of .the lateral section of the plate, is mounted in a plane which is perpendicular thereto.

This loop'forms in itself a closed contour and is welded to the plate'B at thepoint D. Upon the loop so mounted a small piece of metallic getter, or other material that it is desired to vaporize, may be attached to loop C at E. When the high frequency coil is applied over the bulb in a tube to which the loop has been mounted in this position the electrodes become heated while the loop itself remainspcomparatively cool and far below the vaporization point of the attached niaterial, and the electrodes are thus degasifled while I the metallic getter remains unvolatiliaed. blow,

It has been -in said body is shielded by eases the. degasification of the electrodes being completed, the high frequency'coil may be removed be attached to the metal parts of such electrical devices, the loops being-set at various angles to the plane of the lateral sectionof the part to which it is attached as shown in Fig. -3. In this form of the invention one loop 0 is mounted upon the grid electrode supports D, similar to the arrangement shown in Fig. l, and a second loop C is mounted upon the plate electrode support D such that the plane of loop C is disposed at an angle to the plane of loop C. By arranging the loops C and C in this manner they are individually susceptible to magnetic fields of different directions. Preferably the loop C carries a globule E of vaporizable material to be used as a getter.

Having thus described my invention what I claim is:

1. The method of removing gas from a conductive body inclosed within an envelope wherenother conductive body from a magnetic field w ch consists in affixing to said first mentioned body a loop of conductive material forming a closed contour with said body and being insulated from other conductive bodies within said envelope heating said' loop and said conductive body bya high frequency said envelope.

2. The method of degasifying conductive bodies shielded by other conductive bodies within' an envelope which consists in attaching a loop of conductive material to the body to be degasified insuch manner that the loop and said body combine to form a closed contour, said loop being insulated from the other conductive bodies within said envelope, heating said loop and the body to be degasifled by the action of a high frequency magnetic field, the magnetic flux of which is perpendicular to the plane of saidloop, and cuts the loop beyond the shielding influence of the other conductive bodies removing the gases fromsaid conductive body by such heating, removing such gases from the envelope and sealing said envelope. v

3. The method of degasiiylng, the grid electrodes of radio vacuum tubes, having a plurality of inclosed electrodes including a grid inclosed within a plate electrode. all inclosed within an envelope, which consists in attaching to thegrid supports a loop so shaped as to extend outward following in part the contour of the edge of the plate and forming with the portions of the grid opposite said loop a closed contour, heating said loop and said grid by a high frequency magnetic field to remove the gas therefrom, removing said gas from said envelope, and sealing said envelope. 4. The method of preparing electrical discharge devices having conductive bodies inclosed within an envelope. which consists in afllxing to one of said conductive bodies a loop having a closed contour lying in a plane transverse to the axis of ductive bodies by a high frequenc magnetic field g to remove the gas therefrom while said loop remains relatively cool, afterwards heating said loop by a high frequency magnetic field to the vaporization point of the substance attached I contour, heating said loop and said shielded electrode by a high frequency magnetic field to drive out the occluded gases from said shielded electrode, removing said gases from said envelope and sealing saidenvelope. v

6. The method of improving the vacuum within the envelope of an electrical discharge device having conductive bodies inclosed within said envelope which consists in attaching to one of said electrodes a loop of conductive material in a plane perpendicular to the plane of a lateral section of said electrodes and afllxing to said loop a getter, heating said electrodes by means of a high frequency magnetic field to drive out the occluded gases from said electrodes while the loop remainsat a temperature below the vapor ization temperature of the getter, then heating the loop by a high frequency magnetic field to the vaporization point of said getter while the electrodes are at a temperature below said vaporization point, removing the residual gases from the envelope and sealing said envelope.

7. The method of preparing electrical discharge devices having electrodes inclosed within an envelope which consists in attaching a vaporizable substance to a loop which is ailixed to one of the electrodes by inductive heating, driving out from the electrodes the occluded gases then vaporizing said vaporizable substances by inductive heating, removing the residual gases from said envelope and sealing said envelope.

8. The method of preparing electrical discharge devices having electrodes inclosed within an envelope which consists in attaching a vaporizable substance to a loop which is amxed to one of theelectrodes, then by the action of a high frequency magnetic field, driving out from the electrodes the occluded gases and vaporizing the said vaporizable substances at different times, removing residual gases from said envelope and sealing said envelope.

9. In an electrical discharge device having conductive bodies sealed within an envelope, one of said conductive bodies being shielded from the influence of a magnetic flux by another of said conductive bodies, an exposed loop having an effectively closed contour attached to said shielded conductive body which is desired to be heated inductively.

10, In an electrical discharge device having conductive bodies sealed within an envelope, one oi said conductive bodies being shielded from the influence of a magnetic flux by another of said conductive bodies, an exposed loop of conductive material attached to said shielded conductive body which is desired to be heated inductively,

said loop forming in combination with the part to which it is attached a closed contour.

11. In an electrical discharge device having conductive bodies sealed within an envelope a loop of conductive material having a closed contour to which is ailixed a substance to be vaporized, said loop being in 8. axis of said conductive bodies.

12. In a radio vacuum tube having a filament and grid inclosed within aplate electrode, all of said electrodes being inclosed within an envelope, a-loop of conductive material having a closed contour attached to the grid supports, said loop lying ina plane perpendicular to the axis of said grid.

plane parallel to the 13. In a radio vacuum tube having a filament and grid inclosed within a plate, all of said electrodes being inclosed within an envelope, and said grid being shielded by the plate from the infiuence of a magnetic flux, an exposed loop of conductive material attached to the grid supports and forming with one side of the grid a closedcontour. g I

. 14. In an electrical discharge device having electrodes inclosed within an envelope, one of the electrodes being shielded by another electrode from the influence of a magnetic flux, an exposed loop of conductive material attached to said shielded electrode and forming with said electrode a closed contour susceptible to the influence of a magnetic fiux of a given direction, and a sec- I ond loop of conductive material attached to one of the electrodes and exposed at an angle to said first mentioned loop, said second mentioned loop having a closed contour and being disposed so as to be susceptible to the influence of a.second magnetic flux disposed at an angle. to the first mentioned flux.

15. The method of preparing electrical discharge devices having electrically conductive bodies comprising electrodes disposed within an exhausted envelope, which consists in first so directing an intense high frequency magnetic field from without said envelope that the entire mass of each of said electrodes is heated chiefly by high frequency currents induced in each of said electrodes by said high frequency magnetic field to such elevated temperature and for a sufficient time, so as to expel substantially all re-- movable gases therefrom, discontinuing such heating of said electrodes to permit them to cool, and thereafter without any concurrent appreciable reheating of any of said previously heated electrodes so directing a differently disposed intense high-frequency magnetic field from without said envelope as to inductively so heat an electrically conductive getter support, which sup port is of miniature mass in comparison to the mass of said electrodes and was previously prop erly positioned in said envelope close to but spaced apart from any of said electrodes, to such elevated temperature and for a sufiicient time, but without concurrent appreciable additional degasification of said electrodes, so as to vaporize a getter disposed in good thermal conducting contact with said support, removing the residual gas from said envelope, and sealing said envelope.

16-. The method oi preparing electrical discharge. devices having electrically conductive bodies comprising electrodes disposed within an exhausted envelope, which consists in so directing a high frequency magnetic field from a coil disposed exteriorly of said envelope to inductively heat said electrodes for a suflicient time and to such an elevated temperature, as to remove substantially all gases therefrom chiefly directly by saidinductive heating, then discontinuing such heating of said electrodes and permitting them to cool, and thereafter, and without any appreciable reheating of said electrodes, directing a difierently disposes? high irequency magnetic field from a coil also exteriorly located in respect to said envelope as to independently,

inductively heat a getter previously disposed within said envelope prior to the initial exhausting of saidenvelope in a position close to but spaced apart from any of said electrodes, for a sufilcient time and to such elevated temperature as to vaporize said getter, said getter being of relatively miniature mass as compared to the aggregate mass of said electrodes, the heating of in an envelope, which consists in directing a high frequency electric current in a circuitous path so disposed as to embrace said envelope and thereby electromagnetically induce heating currents in said metal parts within said envelope cases which are embraced within said path to remove the gases from said thereby heated parts chiefly by the direct eflect of said inductive heating, then permitting said heated parts to cool, and later, without appreciably reheating said parts, vaporizing a getter amxed to another metal part previously also enclosed within said envelope in a' position close to but spaced apart from any of said first named metal parts, which getter bearing part is 01 negligibly small mass compared to the mass of said first named metal parts, by directing high frequency electrical currents through a circuitous path, which path is disposed difierently from said first mentioned path disposition, in .order to set up a high frequency magnetic fleld to .cause said held to induce electromagnetically heating electric currents in said getter bearing part to vaporize said getter while said first named metal parts remain cool, thus effecting independent sequential selective inductive heating of said first heated parts and 01 said.

getter both by high frequency currents directed in different circuitous paths disposed without said 7 envelope, removing the-residual gas from said envelope, and sealing said envelope.

ALEXANDER RAVA. 

